Saturated heterocycles are significant structural components of a wide range of drugs. Drug action depends strongly on the conformational properties of the heterocycle substrate, both in the free state and in the receptor bound state. Two new potentially useful families of drugs are the thiosugars and the homopiperazines. We are carrying out the first comprehensive conformational studies of these systems, comparing them to the older families of pharmaceutically important saturated heterocycles, such as the natural sugars, the piperidines, and the piperazines. In addition, we are using piperidines and 1,3-oxazolidines to examine conformational changes, both static and dynamic, that occur as the small molecule is complexed with relatively large molecules. These studies will shed new light on the role of conformation in drug action.